This is useful for if you need to wait for a certain number of users to be in a queue before they can be returned randomly as a group - it must be two more more users.

Let's say you are playing a game and you need 2 players before you can start. You can wait until the queue is ready with at least 2 players and then the system will pair them up accordingly. The paired players will be released from the queue and you can retrieve them by their group key.